At present, vehicle engines are often suspended, pendulum-like in the chassis, with the engine unit being fixed about an axis that is parallel to the crank shaft axis. A link is therefore required for connecting the engine unit to the chassis in order to take up engine torque while the engine is accelerating or decelerating.
FIG. 1 of the accompanying drawings is a diagram showing how such a torque take-up link, referenced 1, is installed to connect the engine unit 2 to the chassis 3 of the vehicle, said link having hinged ends 4 and 5. The pendulum axis is referenced 6 and the anti-vibration pads are referenced 7'.
Such a torque take-up link must filter engine vibration so as to transmit as little vibration as possible to the body of the vehicle.
FIG. 2 of the accompanying drawings shows the desired curve of force (F) as a function of displacement (d) with positive force representing traction and negative force representing compression. It can be seen that about the equilibrium point O the stiffness of such a link should be practically zero, while becoming very much greater whenever the absolute value of the force increases.
In certain applications, there is a need for a two-stage curve, as shown in FIG. 3. In this case, it can be seen that the slope of the graph of .vertline.F.vertline.=f(d) increases suddenly at two occasions between zones (a) and (b) and between zones (b) and (c).
Another essential function of torque take-up links is to take up a very large accidental traction or compression force without deforming [zone referred to below as (c)].
Present torque take-up links are made of multiple materials. The stiffness curve is obtained by one or more rubber pads. The maximum traction or compression force is taken up by a strength member that may be made of steel, aluminum, or an engineering polymer.
The generalization of catalytic converters means an increase in engine power and a rise in temperature in the engine compartment. The increase in engine power gives rise to an increase in the maximum force that is exerted on the link. In addition, car manufacturers seek to reduce vehicle weight but without changing the size of the members situated in the engine compartment.
It is therefore necessary to find the best possible compromise between size, maximum force on breaking, and weight.
A steel strength member makes it possible to obtain a solution that is quite compact but that is penalized by its heavy weight.
When using a link with two stiffness stages, one stage on each axis, a steel strength member has the drawback of giving rise to resonance at rather low frequencies.
An aluminum strength member makes it possible to reduce the weight of the link relative to a steel strength member. However the increase in maximum force on breaking requires it to be of such a size as to be bulky.
The loss of mechanical characteristics suffered by engineering polymers with increasing temperature needs the strength member to be of such a size as to become bulky. The available space is then often exceeded.